Methods and compositions for controlling biofouling using oxime esters

ABSTRACT

The present invention relates to a method to inhibit bacteria from adhering to a submergible surface. The method contacts the submergible surface with an effective amount of at least one oxime ester to inhibit bacterial adhesion to the submergible surface. The present invention also relates to a method for controlling biofouling of an aqueous system. This method adds an effective amount of at least one oxime ester to inhibit bacteria from adhering to a submerged surface within the aqueous system.. This method effectively controls biofouling without substantially killing the bacteria. The oxime ester used in the method of the invention has the following formula: ##STR1## The present invention also relates to compositions containing oxime esters and useable in the above methods. The compositions comprise at least one oxime ester in an amount effective to inhibit bacteria from adhering to submergible or submerged surfaces.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention uses oxime esters to inhibit bacterial adhesion tosubmergible or submerged surfaces, particularly those surfaces within anaqueous system. The invention also relates to methods and compositionsfor controlling biological fouling.

2. Description of Related Art

Microorganisms adhere to a wide variety of surfaces, particularlysurfaces in contact with aqueous fluids which provide a suitableenvironment for microbial growth. For example, microorganisms are knownto adhere to ship hulls, marine structures, teeth, medical implants,cooling towers, and heat exchangers. Adhering to such submerged orsubmergible surfaces, microorganisms may foul the surface or cause it todeteriorate.

In mammals, (e.g., humans, livestock, pets), microorganisms adhered to asurface may lead to health problems. Plaque, for example, results frommicroorganisms adhering to the surfaces of teeth. Medical implants withunwanted microorganisms adhered to their surfaces often become crustedover and must be replaced.

Scientific studies have shown that the first stage of biofouling inaqueous systems is generally the formation of a thin biofilm onsubmerged or submergible surfaces, i.e., surfaces exposed to the aqueoussystem. Attaching to and colonizing on a submerged surface,microorganisms such as bacteria, are generally thought to form thebiofilm and modify the surface to favor the development of the morecomplex community of organisms that make up the advanced biofouling ofthe aqueous system and its submerged surfaces. A general review of themechanisms of the importance of biofilm as the initial stage inbiofouling is given by C. A. Kent in "Biological Fouling: Basic Scienceand Models" (in Melo, L. F., Bott, T. R., Bernardo, C. A. (eds.),Fouling Science and Technology, NATO ASI Series, Series E, AppliedSciences: No. 145, Kluwer Acad. Publishers, Dordrecht, The Netherlands,1988). Other literature references include M. Fletcher and G. I. Loeb,Appl. Environ. Microbiol 37 (1979) 67-72; M. Humphries et. al., FEMSMicrobiology Ecology 38 (1986) 299-308; and M. Humphries et. al., FEMSMicrobiology Letters 42 (1987) 91-101.

Biofouling, or biological fouling, is a persistent nuisance or problemin a wide varieties of aqueous systems. Biofouling, both microbiologicaland macro biological fouling, is caused by the buildup ofmicroorganisms, macro organisms, extracellular substances, and dirt anddebris that become trapped in the biomass. The organisms involvedinclude microorganisms such as bacteria, fungi, yeasts, algae, diatoms,protozoa, and macro organisms such as macro algae, barnacles, and smallmollusks like Asiatic clams or Zebra Mussels.

Another objectionable biofouling phenomenon occurring in aqueoussystems, particularly in aqueous industrial process fluids, is slimeformation. Slime formation can occur in fresh, brackish or salt watersystems. Slime consists of matted deposits of microorganisms, fibers anddebris. It may be stringy, pasty, rubbery, tapioca-like, or hard, andhave a characteristic, undesirable odor that is different from that ofthe aqueous system in which it formed. The microorganisms involved inslime formation are primarily different species of spore-forming andnonspore-forming bacteria, particularly capsulated forms of bacteriawhich secrete gelatinous substances that envelop or encase the cells.Slime microorganisms also include filamentous bacteria, filamentousfungi of the mold type, yeast, and yeast-like organisms.

Biofouling, which often degrades an aqueous system, may manifest itselfas a variety of problems, such as loss of viscosity, gas formation,objectionable odors, decreased pH, color change, and gelling.Additionally, degradation of an aqueous system can cause fouling of therelated water-handling system, which may include, for example, coolingtowers, pumps, heat exchangers, and pipelines, heating systems,scrubbing systems, and other similar systems.

Biofouling can have a direct adverse economic impact when it occurs inindustrial process waters, for example in cooling waters, metal workingfluids, or other recirculating water systems such as those used inpapermaking or textile manufacture. If not controlled, biologicalfouling of industrial process waters can interfere with processoperations, lowering process efficiency, wasting energy, plugging thewater-handling system, and even degrade product quality.

For example, cooling water systems used in power plants, refineries,chemical plants, air-conditioning systems, and other industrialoperations frequently encounter biofouling problems. Airborne organismsentrained from cooling towers as well as waterborne organisms from thesystem's water supply commonly contaminate these aqueous systems. Thewater in such systems generally provides an excellent growth medium forthese organisms. Aerobic and heliotropic organisms flourish in thetowers. Other organisms grow in and colonize such areas as the towersump, pipelines, heat exchangers, etc. If not controlled, the resultingbiofouling can plug the towers, block pipelines, and coat heat-transfersurfaces with layers of slime and other biologic mats. This preventsproper operation, reduces cooling efficiency and, perhaps moreimportantly, increases the costs of the overall process.

Industrial processes subject to biofouling also include papermaking, themanufacture of pulp, paper, paperboard, etc. and textile manufacture,particularly water-laid non-woven textiles. These industrial processesgenerally recirculate large amounts of water under conditions whichfavor the growth of biofouling organisms.

Paper machines, for example, handle very large volumes of water inrecirculating systems called "white water systems." The furnish to apaper machine typically contains only about 0.5% of fibrous andnon-fibrous papermaking solids, which means that for each ton of paperalmost 200 tons of water pass through the headbox. Most of this waterrecirculates in the white water system. White water systems provideexcellent growth media for biofouling microorganisms. That growth canresult in the formation of slime and other deposits in headboxes,waterlines, and papermaking equipment. Such biofouling not only caninterfere with water and stock flows, but when loose, can cause spots,holes, and bad odors in the paper as well as web breaks--costlydisruptions in paper machine operations.

Biofouling of recreational waters such as pools or spas or decorativewaters such as ponds or fountains can severely detract from people'senjoyment of them. Biological fouling often results in objectionalodors. More importantly, particularly in recreational waters, biofoulingcan degrade the water quality to such an extent that it becomes unfitfor use and may even pose a health risk.

Sanitation waters, like industrial process waters and recreationalwaters, are also vulnerable to biofouling and its associated problems.Sanitation waters include toilet water, cistern water, septic water, andsewage treatment waters. Due to the nature of the waste contained insanitation waters, these water systems are particularly susceptible tobiofouling.

To control biofouling, the art has traditionally treated an affectedwater system with chemicals (biocides) in concentrations sufficient tokill or greatly inhibit the growth of biofouling organisms. See, e.g.,U.S. Pat. Nos. 4,293,559 and 4,295,932. For example, chlorine gas andhypochlorite solutions made with the gas have long been added to watersystems to kill or inhibit the growth of bacteria, fungi, algae, andother troublesome organisms. However, chlorine compounds may not onlydamage materials used for the construction of aqueous systems, they mayalso react with organics to form undesirable substances in effluentstreams, such as carcinogenic chloromethanes and chlorinated dioxins.Certain organic compounds, such as methylenebis- thiocyanate,dithiocarbamates, haloorganics, and quaternary ammonium surfactants,have also been used. While many of these are quite efficient in killingmicroorganisms or inhibiting their growth, they may also be toxic orharmful to humans, animals, or other non-target organisms.

One possible way to control the biofouling of aqueous systems, whichinclude the associated submerged surfaces, would be to prevent orinhibit bacterial adhesion to submerged surfaces within the aqueoussystem. This can be done, of course, using microbicides which, however,generally suffer from some of the disadvantages mentioned above. As analternative, the present invention provides methods and compositionsuseful to substantially inhibit bacterial adhesion to a submerged orsubmergible surface and in controlling biofouling of aqueous systems.The invention obviates the disadvantages of prior methods. Otheradvantages of this invention will become apparent from a reading of thespecifications and appended claims.

SUMMARY OF THE INVENTION

The present invention relates to a method to inhibit bacteria fromadhering to a submergible surface. The method contacts the submergiblesurface with an effective amount of at least one oxime ester to inhibitbacteria from adhering to a submergible surface. The oxime ester used inthe method has the following formula: ##STR2## The substituents R¹ andR² may each independently be a methyl group, an ethyl group, or, withthe carbon atom carrying them, form a cyclopentyl group or a cyclohexylgroup. The substituent R³ is a C₅ -C₁₉ alkyl group.

The present invention relates also to a method for controllingbiofouling of an aqueous system. This method adds to an aqueous systeman effective amount of at least one oxime ester described above toinhibit bacteria from adhering to submerged surfaces within the aqueoussystem. This method effectively controls biofouling withoutsubstantially killing the bacteria.

The present invention also relates to a composition for controllingbiofouling of an aqueous system. The composition comprises at least oneoxime ester in an amount effective to inhibit bacteria from adhering toa submergible surface or a submerged surface within the aqueous system.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, this invention relates to a method to inhibitbacteria from adhering to a submergible surface. A submergible surfaceis one which may at least partially be covered, overflowed, or wettedwith a liquid such as water or another aqueous fluid or liquid. Thesurface may be intermittently or continually in contact with the liquid.As discussed above, examples of submergible surfaces include, but arenot limited to, ship or boat hulls, marine structures, teeth, medicalimplants, surfaces within an aqueous system such as the inside of apump, pipe, cooling tower, or heat exchanger. A submergible surface maybe composed of hydrophobic, hydrophilic, or metallic materials.Advantageously, using an oxime ester according to the invention caneffectively inhibit bacteria from adhering to hydrophobic, hydrophilic,or metallic submergible or submerged surfaces.

To inhibit the adhesion of a bacteria to a submergible surface, themethod contacts the submergible surface with an oxime ester. The surfaceis contacted with an effective amount of an oxime ester, or mixture ofoxime esters, to inhibit bacterial adhesion to the surface. The oximeester may be applied to the submergible surface using means known in theart. For example as discussed below, the oxime ester may be applied byspraying, coating or dipping the surface with a liquid formulationcontaining the oxime ester. Alternatively, the oxime ester may beformulated as a paste which is then spread or brushed on the submergiblesurface. Advantageously, the oxime ester may be a component of acomposition or formulation commonly used with a particular submergiblesurface.

"Inhibiting bacteria from adhering" to a submergible surface means toallow a scant or insignificant amount of bacterial adhesion for adesired period of time. Preferably, essentially no bacteria adhesionoccurs and more preferably, it is prevented. The amount of oxime esteremployed should allow only scant or insignificant bacterial adhesion andmay be determined by routine testing. Preferably, the amount of oximeester used is sufficient to apply at least a monomolecular film of oximeester to the submergible surface. Such a film preferably covers theentire submergible surface.

Contacting a submergible surface with an oxime ester according to thismethod allows the surface to be pretreated against bacterial adhesion.Accordingly, the surface may be contacted with an oxime ester thensubmerged in an aqueous system.

The present invention relates also to a method for controllingbiofouling of an aqueous system. An aqueous system comprises not onlythe water or aqueous fluid or liquid flowing through the system but alsothe submerged surfaces associated with the system. Like the submergiblesurfaces discussed above, submerged surfaces are those surfaces incontact with the aqueous fluid or liquid. Submerged surfaces include,but are not limited to, the inside surfaces of pipes or pumps, the wallsof a cooling tower or headbox, heat exchangers, screens, etc. In short,surfaces in contact with the aqueous fluid or liquid are submergedsurfaces and are considered part of the aqueous system.

The method of the invention adds at least one oxime ester to the aqueoussystem in an amount which effectively inhibits bacteria from adhering toa submerged surface within the aqueous system. At the concentrationused, this method effectively controls biofouling of the aqueous systemwithout substantially killing the bacteria.

"Controlling biofouling" of the aqueous system means to control theamount or extent of biofouling at or below a desired level and for adesired period of time for the particular system. This can eliminatebiofouling from the aqueous system, reduce the biofouling to a desiredlevel, or prevent biofouling entirely or above a desired level.

According to the present invention, "inhibiting bacteria from adhering"to a submerged surface within the aqueous system means to allow a scantor insignificant amount of bacterial adhesion for a desired period oftime for the particular system. Preferably, essentially no bacterialadhesion occurs and more preferably, bacterial adhesion is prevented.Using an oxime ester according to the invention can, in many cases,break up or reduce other existing attached microorganisms toundetectable limits and maintain that level for a significant period oftime.

While some oxime esters may exhibit biocidal activity at concentrationsabove certain threshold levels, oxime esters effectively inhibitbacterial adhesion at concentrations generally well below such thresholdlevels. According to the invention, the oxime ester inhibits bacterialadhesion without substantially killing the bacteria. Thus, the effectiveamount of an oxime ester used according to the invention is well belowits toxic threshold, if the oxime ester also has biocidal properties.For example, the concentration of the oxime ester used may be ten ormore times below its toxic threshold. Preferably, the oxime ester shouldalso not harm non-target organisms which may be present in the aqueoussystem.

An oxime ester, or a mixture of oxime esters, may be used to controlbiofouling in a wide variety of aqueous systems such as those discussedabove. These aqueous systems include, but are not limited to, industrialaqueous systems, sanitation aqueous systems, and recreational aqueoussystems. As discussed above, examples of industrial aqueous systems aremetal working fluids, cooling waters (e.g., intake cooling water,effluent cooling water, and recirculating cooling water), and otherrecirculating water systems such as those used in papermaking or textilemanufacture. Sanitation aqueous systems include waste water systems(e.g., industrial, private, and municipal waste water systems), toilets,and water treatment systems, (e.g., sewage treatment systems). Swimmingpools, fountains, decorative or ornamental pools, ponds or streams,etc., provide examples of recreational water systems.

The effective amount of an oxime ester used to inhibit bacteria fromadhering to a submerged surface in a particular system will varysomewhat depending on the aqueous system to be protected, the conditionsfor microbial growth, the extent of any existing biofouling, and thedegree of biofouling control desired. For a particular application, theamount of choice may be determined by routine testing of various amountsprior to treatment of the entire affected system. In general, aneffective amount used in an aqueous system may range from about 1 toabout 500 parts per million and more preferably from about 20 to about100 parts per million of the aqueous system.

The oxime esters employed in the present invention have the followinggeneral formula: ##STR3## The substituents R¹ and R² may eachindependently be a methyl group, an ethyl group, or, with the carbonatom carrying them, form a cyclopentyl or a cyclohexyl group.Preferably, R¹ and R² are methyl or ethyl and more preferably, both R¹and R² are methyl. The substituent R³ is a C₅ -C₁₉ alkyl group.Preferably, R³ is a C₈ -C₁₇ alkyl and more preferably, a C₇, C₈, C₁₁,C₁₃, C₁₅, or C₁₇ alkyl group. The R¹ alkyl group may be bound through aterminal carbon or a carbon in the alkyl chain. The alkyl group may alsobe branched or unbranched. Specific preferred oxime esters includeO-myristoyl acetoxime, compound a; O-palmitoyl acetoxime, compound b;CASRN 139745-12-3; O-2-ethylhexanoyl acetoxime, compound c; O-nanoylacetoxime, compound d; O-stearaoyl acetoxime, compound e.

The oxime esters employed in the invention may be prepared usingtechniques known in the art. For example, an acid chloride may bereacted with an oxime. For example, Aranda et al. describe the synthesisof O-palmitoyl acetoxime, compound b, using this synthesis reactinghexadecanoyl chloride and propan-2-one oxime (or acetone oxime). Arnandaet al., Synth. Commun. 22, 1992, 135-144.

The methods according to the invention may be part of an overall watertreatment regimen. The oxime ester may be used with other watertreatment chemicals, particularly with biocides (e.g., algicides,fungicides, bactericides, molluscicides, oxidizers, etc.), stainremovers, clarifiers, flocculants, coagulants, or other chemicalscommonly used in water treatment. For example, submergible surfaces maybe contacted with an oxime ester as a pretreatment to inhibit bacterialadhesion and placed in aqueous system using a microbicide to control thegrowth of microorganisms. Or, an aqueous system experiencing heavybiological fouling may first be treated with an appropriate biocide toovercome the existing fouling. An oxime ester may then be employed tomaintain the aqueous system. Alternatively, an oxime ester may be usedin combination with a biocide to inhibit bacteria from adhering tosubmerged surfaces within the aqueous system while the biocide acts tocontrol the growth of microorganisms in the aqueous system. Such acombination generally allows less microbicide to be used.

"Controlling the growth of the microorganisms" in an aqueous systemmeans control to, at, or below a desired level and for a desired periodof time for the particular system. This can be eliminating themicroorganisms or preventing their growth in the aqueous systems.

The oxime ester may be used in the methods of the invention as a solidor liquid formulation. Accordingly, the present invention also relatesto a composition containing an oxime ester. The composition comprises atleast one oxime ester in an amount effective to inhibit bacteria fromadhering to a submergible surface or a submerged surface within anaqueous system. When used in combination with another water treatmentchemical such as a biocide, the composition may also contain thatchemical. If formulated together, the oxime ester and water treatmentchemical should not undergo adverse interactions that would reduce oreliminate their efficacy. Separate formulations are preferred whereadverse interactions may occur.

Depending on its use, a composition according to the present inventionmay be prepared in various forms known in the art. For example, thecomposition may be prepared in liquid form as a solution, dispersion,emulsion, suspension, or paste; a dispersion, suspension, or paste in anon-solvent; or as a solution by dissolving the oxime ester in a solventor combination of solvents. Suitable solvents include, but are notlimited to, acetone, glycols, alcohols, ethers, or otherwater-dispersible solvents. Aqueous formulations are preferred.

The composition may be prepared as a liquid concentrate for dilutionprior to its intended use. Common additives such as surfactants,emulsifiers, dispersants, and the like may be used as known in the artto increase the solubility or compatability of the oxime ester or othercomponents in a liquid composition or system, such as an aqueouscomposition or system. In many cases, the composition of the inventionmay be solubilized by simple agitation. Dyes or fragrances may also beadded for appropriate applications such as toilet waters.

A composition of the present invention may also be prepared in solidform. For example, the oxime ester may be formulated as a powder ortablet using means known in the art. The tablets may contain a varietyof excipient known in the tableting art such as dyes or other coloringagents, and perfumes or fragrances. Other components known in the artsuch as fillers, binders, glidants, lubricants, or antiadherents mayalso be included. These latter components may be included to improvetablet properties and/or the tableting process.

The following illustrative examples are given to disclose the nature ofthe invention more clearly. It is to be understood, however, that theinvention is not limited to the specific conditions or details set forthin those examples.

EXAMPLES Example 1: Preparation of O-Muristoyl Acetoxime, Compound a

Under a nitrogen blanket, acetone oxime, 3.0 g; triethylamine, 4.1 g;and 20 ml dry CH₂ Cl₂, were placed in a 100 ml, 3 neck round bottomflask fitted with a claison adapter having a reflux condenser with anitrogen inlet and an addition funnel, thermometer, magnetic stir bar,and a septum. The flask and its contents were chilled to 0° C. Myristoylchloride, 4.0 g, and 25 ml dry CH₂ Cl₂ was placed in the additionfunnel. The myristoyl chloride solution was then added slowly to thestirring acetone oxime solution such that the reaction temperature didnot rise above 5° C. After the addition was complete, the reaction wasallowed to warm to room temperature and stirred overnight. The resultingclear solution was diluted with 50 ml CH₂ Cl₂, washed 1×10 ml with 5%HCl, 1×10 ml with 5% KOH, and finally 3×10 ml water. The organic layerwas separated from the aqueous layer, dried over MgSO₄, and filtered.The organic solvent was then evaporated to afford 3.3 g of light yellowoil product. The product was identified using ¹³ C NMR spectroscopy.

Example 2: Inhibition of Bacterial Adhesion

Test Method: The following method effectively defines the ability of achemical compound to inhibit bacterial adhesion, or attack the formationof existing attached bacteria, on various types of surfaces. As anoverview, bioreactors were constructed in which approximately 1 in.×3in. slides (glass or polystyrene) were fixed to the edge of thebioreactor. The lower ends (approx. 2 in.) of the slides dipped into abacterial growth medium (pH 7) within the bioreactor which contained aknown concentration of the test chemical. Following inoculation withknown bacterial species, the test solutions were stirred continuouslyfor 3 days. Unless otherwise indicated in the results below, the mediumwithin the bioreactor was turbid by the end of three days. Thisturbidity indicated that the bacteria proliferated in the medium despitethe presence of the chemical tested. This also shows that the chemical,at the concentration tested, showed substantially no biocide(bactericidal) activity. A staining procedure was then used on theslides in order to determine the amount of bacteria attached to thesurfaces of the slides.

Construction of Bioreactors: The bioreactors comprised a 400 ml glassbeaker over which a lid (cover from a standard 9 cm diameter glass petridish) was placed. With the lid removed, slides of the material of choicewere taped at one end with masking tape and suspended inside thebioreactor from the top edge of the beaker. This allows the slides to besubmerged within the test medium. Typically, four slides (replicates)were uniformly spaced around the bioreactor. The score presented beloware the average of the four replicates. A magnetic stirring bar wasplaced in the bottom of the unit, the lid positioned, and the bioreactorautoclaved. Two different types of material were used as slides,polystyrene (polystyr.) as a hydrophobic surface and glass as ahydrophillic surface.

Bacterial Growth Medium: The liquid medium utilized in the bioreactorswas described previously by Delaquis, et al., "Detachment Of Pseudomonasfluorescens From Biofilms On Glass Surfaces In Response To NutrientStress", Microbial Ecology 18:199-210, 1989. The composition of themedium was:

    ______________________________________                                        Glucose               1.0    g                                                K.sub.2 HPO.sub.4     5.2    g                                                KH.sub.2 PO.sub.4     2.7    g                                                NaCl                  2.0    g                                                NH.sub.4 Cl           1.0    g                                                MgSO.sub.4 · 7H.sub.2 O                                                                    0.12   g                                                Trace Element         1.0    ml                                               Deionized H.sub.2 O   1.0    L                                                ______________________________________                                    

    ______________________________________                                        CaCl.sub.2            1.5    g                                                FeSO.sub.4 · 7H.sub.2 O                                                                    1.0    g                                                MnSO.sub.4 · 2H.sub.2 O                                                                    0.35   g                                                NaMoO.sub.4           0.5    g                                                Deionized H.sub.2 O   1.0    L                                                ______________________________________                                    

The medium was autoclaved and then allowed to cool. If a sediment formedin the autoclaved medium, the medium was resuspended by shaking beforeuse.

Preparation of Bacterial Inocula: Bacteria of the genera Bacillus,Flavobacterium, and Pseudomonas were isolated from a paper mill slimedeposit and maintained in continuous culture. The test organisms wereseparately streaked onto plate count agar and incubated at 30° C. for 24hours. With a sterile cotton swab, portions of the colonies were removedand suspended in sterile water. The suspensions were mixed very well andwere adjusted to an optical density of 0.858 (Bacillus), 0.625(Flavobacterium), and 0.775 (Pseudomonas) at 686 nm.

Biofilm Production / Chemical Testing: To four separate bioreactors wasadded 200 ml of the sterile medium prepared above. Compounds to beevaluated were first prepared as a stock solution (40 mg /2 ml) usingeither water or a 9:1 acetone: methanol mixture (ac/MeOH) as a solvent.A 1.0 ml aliquot of the stock solution was added to the bioreactor usingmoderate, continuous magnetic stirring. This provided an initialconcentration of 100 ppm for the test compound. Other concentrationstested for a particular compound are set forth in the Table below. Onebioreactor (Control) contained no test compound. Aliquots (0.5 ml) fromeach of the three bacterial suspensions were then introduced into eachbioreactor. The bioreactors were then provided with continuous stirringfor three days to allow for an increase in bacterial population anddeposition of cells onto the surfaces of the slides.

Evaluation of Results: The following compounds were evaluated using theprocedure described above: O-myristoyl acetoxime, compound a;O-palmitoyl acetoxime, compound b; O-2-ethylhexanoyl acetoxime, compoundc; and O-nanoyl acetoxime, compound d.

After the test was completed, the slides were removed from thebioreactors and positioned vertically to permit air drying. The degreeof adhesion of bacteria to the test surface was then estimated using astaining procedure.

The slides were briefly flamed in order to fix the cells to the surface,and then transferred for two minutes to a container of Gram CrystalViolet (DIFCO Laboratories, Detroit, Mich.). The slides were gentlyrinsed under running tap water and then carefully blotted. The degree ofbacterial adhesion was then determined by visual examination andsubjective scoring of each slide. The intensity of the stain is directlyproportional to the amount of bacterial adhesion. The following scoresare given:

    ______________________________________                                        0 = essentially none  3 = moderate                                            1 = scant             4 = heavy                                               2 = slight                                                                    ______________________________________                                    

Chemical treatments were evaluated relative to the Control whichtypically receive an average score for the four bioreactor slides in the3-4 range. Compounds which receive an average score in the 0-2 rangewere considered effective to prevent bacterial adhesion to the submergedslides. The results are shown in the following Table:

    ______________________________________                                                          Conc.                                                       Compound                                                                              Solvent   (ppm)    MIC.sup.1                                                                           Slides  Score                                ______________________________________                                        a       ac/MeOH   100      >500  glass   0.5                                          ac/MeOH   100            polystyr.                                                                             0                                    b       ac/MeOH   100      >500  glass   0                                            ac/MeOH   60             glass   0                                            ac/MeOH   25             glass   0                                            ac/MeOH   20             glass   0.75                                         ac/MeOH   10             glass   3.25                                         ac/MeOH   5              glass   2.75                                         ac/MeOH   100            polystyr.                                                                             0                                    c       ac/MeOH   100      >500  glass   2                                            ac/MeOH   100            polystyr.                                                                             2.7                                  d       ac/MeOH   100      >100  glass   0                                            ac/MeOH   50             glass   1                                            ac/MeQH   25             glass   1                                            ac/MeOH   20             glass   1.5                                          ac/MeOH   10             glass   3                                            ac/MeOH   5              glass   2.75                                         ac/MeOH   100            polystyr.                                                                             0                                    ______________________________________                                         .sup.1 Minimum inhibitory concentration (MIC) for each compound against       the bacteria E. Aerogenee using an 18 hour Basal Salts test both at pH 6      and at pH 8.                                                             

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited tothose embodiments. Other modifications may be made. The appended claimsare intended to cover any such modifications as fall within the truespirit and scope of the invention.

The claimed invention is:
 1. A method to inhibit bacteria from adheringto a submergible surface comprising the step of contacting thesubmergible surface with at least one oxime ester in an amount effectiveto inhibit bacteria from adhering to the submergible surface, whereinthe oxime ester is a compound of the formula: ##STR4## wherein R¹ and R²may each independently be a methyl group, an ethyl group, or, with thecarbon atom carrying them, form a cyclopentyl group or a cyclohexylgroup; and R³ is a C₅ -C₁₉ alkyl group, and wherein the oxime esterinhibits bacterial adhesion without substantially kiIling the bacteria.2. A method of claim 1, wherein R¹ and R² are methyl or ethyl, and R³ isa C₈ -C₁₇ alkyl group.
 3. A method of claim 1, wherein R¹ and R² aremethyl, and R³ is a C₇, C₈, C₁₁, C₁₃, C₁₅, or C₁₇ alkyl group.
 4. Amethod of claim 1, wherein the oxime ester is O-myristoyl acetoxime,O-palmitoyl acetoxime, O-2-ethylhexanoyl acetoxime, O-nanoyl acetoxime,or O-stearoyl acetoxime.
 5. A method of claim 4, wherein the submergiblesurface is a ship hull, a boat hull, a marine structure, a toothsurface, a medical implant surface or a surface of an aqueous system. 6.A method for controlling biofouling of an aqueous system comprising thestep of adding to the aqueous system at least one oxime ester in anamount effective to inhibit bacteria from adhering to a submergedsurface within the aqueous system, wherein the oxime ester is a compoundof the formula: ##STR5## wherein R¹ and R² may each independently be amethyl group, an ethyl group, or, with the carbon atom carrying them,form a cyclopentyl group or a cyclohexyl group; and R³ is a C₅ -C₁₉alkyl group, and wherein the oxime ester inhibits bacterial adhesionwithout substantially killing the bacteria in the aqueous system.
 7. Amethod of claim 6, wherein R¹ and R² are methyl or ethyl, and R³ is a C₈-C₁₇ alkyl group.
 8. A method of claim 6, wherein R¹ and R² are methyl,and R³ is a C₇, C₈, C₁₁, C₁₃, C₁₅, or C₁₇ alkyl group.
 9. A method ofclaim 6, wherein the oxime ester is O-myristoyl acetoxime, O-palmitoylacetoxime, O-2-ethylhexanoyl acetoxime, O-nanoyl acetoxime, orO-stearoyl acetoxime.
 10. A method of claim 6, wherein the effectiveamount of the oxime ester ranges from 10 ppm to 500 ppm.
 11. A method ofclaim 6, wherein the addition step comprises adding sufficient oximeester to the aqueous system to reduce any existing biofouling in theaqueous system.
 12. A method of claim 6, wherein the aqueous system isan industrial water system.
 13. A method of claim 12, wherein theindustrial water system is selected from a cooling water system, a metalworking fluid system, a papermaking water system, and a textilemanufacture water system.
 14. A method of claim 6, wherein the aqueoussystem is a recreational water system.
 15. A method of claim 14, whereinthe recreational water system is selected from a swimming pool, afountain, an ornamental pond, an ornamental pool, and an ornamentalstream.
 16. A method of claim 6, wherein the aqueous system is asanitation water system.
 17. A method of claim 16, wherein thesanitation water system is selected from a toilet water system, acistern water system, a septic water system, and a sewage treatmentsystem.
 18. A method of claim 16, further comprising the step of addingan effective amount of a biocide to the aqueous system to control thegrowth of a microorganism in the aqueous system.
 19. A method of claim18, wherein the biocide is added prior to the oxime ester tosubstantially reduce any existing biofouling in the aqueous system andthe oxime ester is added to prevent the adhesion of surviving bacteriato a submerged surfaces within the aqueous system.
 20. A method of claim18, wherein a biocide is added concurrently with the oxime ester.
 21. Amethod of claim 18, wherein the microorganism is selected from algae,fungi, and bacteria.
 22. A method of claim 18, wherein said aqueoussystem is selected from an industrial water system, a recreational watersystem, and a sanitation water system.